Oakland claimed Valencia off waivers on Aug. 3, and the infielder hit .284 in 47 games with the A's.
Valencia also proved valuable defensively as he posted a .980 fielding percentage in 55 overall games at third base -- the best among third basemen who played in 50 or more games.
While Valencia has agreed to a new contract, Josh Reddick and Fernando Rodriguez are still eligible for arbitration.
William Boor is a reporter for MLB.com. Follow him on Twitter at @wboor. This story was not subject to the approval of Major League Baseball or its clubs.